Self-contained watt-hour meters for exceedingly heavy loads

ABSTRACT

A watt-hour meter has in its base the circular core of a current transformer, wound with the secondary coil, this coil being connected to the current coil of the meter driving unit. The heavy load-carrying conductors extending through this core as its primary winding are carried by the base and are in the form of oppositely facing &#39;&#39;&#39;&#39;U&#39;&#39;&#39;&#39; bars. A special meter box and terminal block facilitates the connecting of this combination in the circuit being measured. Alternatively it may be mounted at a different position, not in the circuit, in which case closing the cover causes the display of words indicating that it is not in service. Shiftable connection links reverse voltage connections in case the supply and load conductors are interchanged from the more usual arrangement, and also facilitate testing. The service connectors are especially suited for very heavy service conductors. Calibration is of the total self-contained meter, i.e., with current transformer as a part thereof.

Sites ate Burkhart, Jr.

SELF-(IONTAINED WATT-HOUR METERS FOR EXCEEDINGLY HEAVY LOADS 1 Mar. 2,i972 FOREIGN PATENTS OR APPLICATIONS 581,553 7/1933 Germany ..324/1 37Primary Examiner-Alfred E. Smith Attorney-Darbo, Robertson & Vandenburgh[57] ABSTRACT A watt-hour meter has in its base the circular core of acurrent transformer, wound with the secondary coil, this coil beingconnected to the current coil of the meter driving unit. The heavyload-carrying conductors extending through this core as its primarywinding are carried by the base and are in the form of oppositely facingU" bars. A special meter box and terminal block facilitates theconnecting of this combination in the circuit being measured.Alternatively it may be mounted at a different position, not in thecircuit, in which case closing the cover causes the display of wordsindicating that it is not in service. Shiftable connection links reversevoltage connections in case the supply and load conductors areinterchanged from the more usual arrangement, and also facilitatetesting. The service connectors are especially suited for very heavyservice conductors. Calibration is of the total self-contained meter,i.e., with current transformer as a part thereof.

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SELF-CONTAINED WATT-HOUR METERS FOR EXCEEDINGLY HEAVY LOADS INTRODUCTIONWatt-hour meters are familiar items as the electricity meters measuringthe electrical energy consumption at every home. The present applicationis especially'suitable to such meters designed for measuring loads whichare exceptionally heavy for private homes, but which have long presenteda problem when large homes are electrically heated. l-Ieretofore, metersfor loads over about 200 amperes have required a very expensiveinstallation embodying one or more current transformers which wereseparate from the meter and had to be separately installed. Theinstallation involved separately connecting its secondary coil to themeter or a meter socket, and a complex undertaking to cause the heavyload current to pass through the aperture of the core of the currenttransformer, two such transformers usually being used. According to thepresent invention great economy and simplification of installation areachieved by providing a meter with a built-in current transformer, thebuilt-in primary or load-carrying conductors of this transformer beingarranged for easy application of this total combination a unit to aspecially designed terminal block to which the heavy supply and loadconductors leading into the meter box are connected.

The need for more heavy duty metering has been present for many years,and has constantly increased through the years. The assignee of thepresent invention has been a leader in satisfying this need to theextent that it could be satisfied by direct metering. In directmetering, as the term is here used, the entire current or amperage ofthe circuit being metered goes through the current coil of the meteritself. In spite of advances, the limit in this direction seems to havebeen reached at around 200 amperes. At least one suggestion has reachedthe present inventor that there should be a self-contained 300 amperemeter.

With loads above about 200 amperes, and sometimes even below it,metering has been done indirectly, using current transformers applied tothe metered circuit and from which connections ran to the meter. Thecurrent in the circuit being measured did not pass through the meter butit passed instead through a primary conductor or winding of the currenttransformer. Only the lighter amperage of the secondary winding of thiscurrent transformer would then flow through the current coil of themeter. Meters to be used this way were routinely calibrated separately,and only ordinary test currents were required.

This system, which hasbeen used for many years, has been objectionablyexpensive and inconvenient; increasingly so as larger and larger numbersof installations required the specially installed and speciallyconnected current transformers, and special voltage connections neededwhen the service conductors do not go to the meter.

According to the present invention the need for self-contained metersfor loads far beyond 200 amperes is satisfied, and both the expense andthe inconvenience of prior indirect metering previously used for thisare considerably reduced.

Some relatively unexpected advantages have resulted. One is greaterdependability of metering accuracy. In the past, indirect metering hassometimes been inaccurate due to aberrations of current transformers.The current transformers are amazingly uniform, but do have minutevariations, and these would of course make a perfectly accurate metergive an inaccurate reading. The inaccuracy was usually small enough tobe tolerated, but occasional larger inaccuracies were likely to beundetected. With the present invention, theseinaccuracies are avoidedbecause the current transformers are part of the unit routinelycalibrated.

Additional advantages will be apparent from the following descriptionand the drawings.

DESIGNATION OF FIGURES FIGS. 1 and 2 are front views of a meter box witha meter therein, the cover of the box being broken away to show themeter terminals; the meter of FIG. 1 being in the service position, andthe meter of FIG. 2 being in its out of service position.

FIG. 3 is a front view of the structure of FIG. 1, with the box coverremoved and on a larger scale.

FIG. 4 is a. fragmentary view sectionally through the box approximatelyalong the line 4-4 of FIG. 3, showing a side view of the box contents.For the sake ofclarity of illustration, there are some inconsistencieswith other figures.

FIG. 5 is a vertical sectional view through the meter and current coilcombination comprising the heart of the present invention.

FIG. 6 is a rear view of the structure of FIG. 5, as indicated by theline 6-6 of FIG. 5.

FIG. 7 and 8 are sectional views through the current transformer, FIG. 8being approximately on the line 8-8 of FIG. 7 and FIG. 7 beingapproximately on the line 7 -7 of FIG. 6.

FIG. 9 is a sectional view through the box approximately on the line 7-7 of FIG. 3, showing a bottom view of the contents of the box.

FIGS. 10 and 11 are respectively front and vertical sectional views ofthe terminal block facilities of the meter box, as indicated by thelines 10-10 of FIG. 9 and 11-11 of FIG. 10.

BACKGROUND DESCRIPTION In some fundamental respects the embodiments ofthe present invention correspond to practice which has long beenfollowed, although the elements here described include departures fromthe common practice. Thus it has been common to mount a watt-hour meter11 in a metal meter box 12 having a cover 13 through which thebowl-shaped glass cover 14 of the meter 11 projects forwardly. Thusalthough the meter dials and some of the meter mechanism was visiblethrough the glass cover, the meter was thoroughly protected within themetal box. The cover of this box has been conventionally secured closedby some sort of tamperproof mechanical sealing device. Usually conduitsl6 and 17 have extended from the top and bottom of the box, one beingfor the power supply conductors and the other being for the loadconductors, i.e. the conductors leading to the circuit on the load sideof the meter.

Probably the most widely known elements of the meter 11 are the dialpointers 18 by which the meter is read and the disk 19 (FIG. 5) whichrotates generally in accordance with the use of power. The disk 19 isdriven by inductive interaction between it and two electromagnets. Oneis a current magnet 21 and the other is the potential or voltage magnet22. The voltage magnet 22 is energized by a voltage coil 23. The currentmagnet 21 is energized by a current coil 24, the illustrated form beingdifferent from the more common type of current soil. The illustratedform of current coil 24, comprising a substantial number of turns ofmoderately small wire, is the type used when it is connected to acurrent transformer.

Current transformers are used when the circuit being measured isextremely heavily loaded. In other situations, as in most residentialmeters, the current coil is a relatively heavy conductor, perhaps ofonly one or two turns, and the total current in the circuit beingmeasured flows through it. When a current transformer is used, the heavycurrent of the load cir cuit does not pass through the internal metercoils. It flows only through one or more heavy conductors, representedin FIG. 6 (in a very novel form and arrangement) by conductors 26 and27, threading the core of the current transformer. A current transformersuch as transformer 28 has heretofore been quite separate from the meterand may have been located relatively remotely from it. Such a currenttransformer is energized by the current of the circuit being metered,flowing in a heavy conductor threading its core, and in turn hasenergized the current coil 24. The current through the coil 24 is muchsmaller than the current of conductors 26 and 27, but proportionalthereto.

Although the following disclosure offered for public dissemination isdetailed to ensure adequacy and aid understanding, this is not intendedto prejudice that purpose of a patent which is to cover each newinventive concept therein no matter how others may later disguise it byvariations in form or additions or further improvements. The claims atthe end hereof are intended as the chief aid toward this purpose, as itis these that meet the requirement of pointing out the parts,improvements, or combinations in which the inventive concepts are found.

DESCRIPTION OF PRESENT INVENTION According to the present invention, asimplified practical meter combination has been developed which includesas an integrated part of it a current transformer 28 complete withterminal-ended conductors 26 and 27 which energize it. In addition toadvantages in economy of manufacture, there are important advantagesalong the line of being able to handle this complete combination much asthe meters alone have heretofore been handled. Thus as is quite clearfrom FIGS. and 6, the new meter and current transformer combination is aselfsufficicnt unit having its own connecting terminals collectively 29but distinguishable by supplemental designations a, b, c and d, exposedat the rear thereof, in predetermined positions, as seen in FIG. 6.Theoretically this would make it possible to plug in these metercombinations just as simple meters heretofore have been plugged in.Because of the heavy loads, however, it is preferred not to use plug infeatures such as springs, but to use the type of connection andmountings shown in FIGS. 1 and 3 where two of the meter terminals 29 areshown resting on connector block conductors 31 and 32 to which they arefirmly secured by screws or terminal bolts 33.

OUT OF SERVICE POSITION In FIGS. 1 and 3 it is clearly seen that theterminal block conductor 31 connects the meter terminals 290 with upperconductors 36, while terminal block conductor 32 connects meter terminal29d with lower conductors 37, since as seen in FIG. 6, terminals 0 and dare two terminal ends of U-shaped conductor bar 27, it is apparent thatthe conductor bar 27 is connecting the conductors 36 and 37 through thecurrent transformer 28. Thus the meter is connected in the circuit inwhich it is metering.

Sometimes, however, it is desired to have the meter present without itbeing connected in the circuit. This could occur, for example, if themeter is initially installed before the entire load circuit is ready forservice. In this event, the meter would not be positioned as shown inFIGS. 1 and 3, but would instead be positioned as shown in FIG. 2. Inthis instance, the meter terminal 290 is mounted on conductor 31 bymeans of hanger bolt 38. As seen clearly in FIG. 4, the hanger bolt 38may be constantly present and is considerably higher than the terminalbolt 33. Of course, if the meter had previously been installed in itsservice position, the four nuts on the bolts 33 would be unscrewed topermit the meter combination to be lifted off of the bolts 33 and hungon the hanger bolts 38, nuts being applied to these bolts to hold themeter in place. At this time, as clearly seen in FIG. 2, the lower meterterminal 29d does not rest on the terminal conductor 32 but rests nearthe lower end of the terminal conductor 31. It therefore no longercompletes a circuit between service conductors 36 and 37. Under thiscondition, the load conductors will not be energized or hot". It isimportant, however, that there be by-pass provisions so that if itshould be desired for services not to be interrupted, a temporaryby-pass connection can be applied. Conductors 31 and 32 are close to oneanother to make such by-pass convenient. For example, if a meter neededto be tested without interrupting the service, a by-pass could first beapplied at each side in the form of a simple conductive bar (with aninsulated handle) applied to the bolts 39. Then the meter could bereleased and removed for testing, or moved to its upper out of serviceposition as already described.

It is preferable that the meter box cover 13 be provided with a slide41, vertically movable in slideways not shown, and having an aperture init which neatly fits the glass cover 14 of the meter. Thenif the coveris applied while the meter is out of service, this slide 14 must be inits upper position, and it is preferably provided with the legend Out ofService which will be visible, as seen in FIG. 2, under this condition.

One common arrangement of the terminal block conductors 31 and 32 isshown in FIG. 3, one above the other to be connected together through asingle conductor of the meter and current transformer combination. Forthree wire circuits there is another such pair 31, 32 at the other sideof the assembly. Both by custom and for technical considerations, thesupply conductors 37 ofien enter at the bottom of the box and the loadconductors 36 at the top, or vice versa. It has been found to bepracticable to provide a simple arrangement of the current transformerfacilities which is compatible with this desirable conductorarrangement. Arrangements can also be made for both the supply and loadconductors to enter at the same end of the box.

CURRENT TRANSFORMER FEATURES Compatibility with the terminal blockconductor locations just described, while at the same time providingproper conductor relationship with the current transformer 28, isachieved by the delightfully simple arrangement seen in FIG. 6. Here itis seen that each of the heavy conductors 26 and 27 is a simple U-shapedbar, the two bars being slipped through the current transformer fromopposite directions. Thus it is seen that the upper leg of each U of thebars 26 and 27 extends through the current transformer 28. Becausecurrent flow at a given moment is in the same direction (left or right)through both of these upper legs, there is the necessary additive effectas to their excitation of the current transformer.

Each of the U-bars 26 and 27 is firmly secured to or as a part of themeter 11 by a floating three point mounting. At each of the three pointsthe mounting is substantially as seen in FIG. 5, where the lowermounting for the bar 26 has been broken away. A mounting post 46 isprovided as an integral part of meter base 47, this meter base beingmolded of an insulating plastic material. A screw 48 extends through thepost 46 and screws into U-bar 26. A conductive spacing sleeve 49surrounds the screw 48. This permits a voltage lead terminal 51 to befirmly clamped between the head of the screw 48 and the sleeve 49. Thevoltage terminal 51 is connected to the voltage coil and a metal-clampedconnection to the terminal 51 is therefore desirable. The metalclampingavoids any danger of deterioration of the voltage connection as theresult of coldflowing of plastic in the course of time as could occur ifthe clamping were dependent upon plastic.

Although the sleeve 49 should be minutely longer than the plasticthrough which it extends, and this might seem to be inconsistent withthe desired predetermined positioning of the terminals 29, there is nosuch difiiculty. Indeed, the minute play possible between the conductors26 and 27 and the plastic base 47 avoids any danger that harmful strainswould be applied to the plastic base in the course of tightening theterminals 29 against the four separate terminal block conductors 31 and32.

' The two bars 26 and 27 serve as the primary winding of the currenttransformer 28, even though they do not have the appearance of awinding. The remainder of the current transformer is preferablypositioned accurately independently of these bars so as to be out ofcontact with them. To this end the meter base 47 is, as seen in FIG. 7,molded with a housing 56 extending rearwardly therefrom. It mayconveniently be opened rearwardly, until filled, and provides a passagefor bars 26 and 27.

The core 57 of the current transformer is preferably strip wound. One ormore long strips of material known as transformer iron are wound uponthemselves spirally to provide a transformer of the desired dimensionsand core characteristics. The secondary winding 58, which is a toroidalwinding, is then wound upon it by known techniques. The completedassembly is inserted in the housing 56 and covered by a molded cap.

In view of the importance of having an economical but dependablysatisfactory current transformer, some details and precautions are herenoted. The transformer core strip is of a type with surface insulationto reduce any eddy currents passing between turns. After coiling, it isannealed at 1400 F. for 2 hours in a dry nitrogen atmosphere. Corners onwhich the winding will bear are rounded and thereafter the core is epoxycoated as by a fluidized bed. A suitable winding has been found to be319 turns, providing three layers of turns on the inside of the core, ofinsulated round copper wire, No. 19 Polythermaleze heavy film being onethat is suitable.

Conductors 26 and 27 are preferably coated with insulation except at theterminals 29 and at the points where the sleeves 49 contact theconductors.

TERMINAL BLOCK CONSTRUCTION Although, of course, the shape and manner ofsupporting and connecting the terminal block conductors 31 and 32 may bevaried, the form illustrated in FIGS. 9 to 11 has been found to be quitesatisfactory. It will be observed from FIG. 9 that the location of U-bar26 rearwardly of the U-bar 27 necessitates having the conductor 31 onthe right closer to the back wall 61 of the box 12 than is the left-handconductor 31. Nevertheless, some identical parts are found on oppositesides. However, metal brackets or benches 62L and 62R are provided whichare identical except for being of different heights. These are securedby screws to the back panel of the meter box 12. To each of these issecured a terminal block assembly, the base portion of which is a moldedinsulative terminal block 66. They may be identically molded, with somedrilled holes at mirror-image positions. As seen in FIG. 10, eachterminal block has four ears 67 through which screws thread into thebench 62R and 62L for securing the terminal block 66 in place. Beforebeing secured in place, each terminal block is provided with theremainder of the terminal block assembly as seen in FIG. 11 except that,if preferred, nuts may be omitted. The essential parts have beendescribed heretofore. For protection from voltage surges such as may beinduced by lightning, spark-gap assemblies 71 may be provided. Each hasone of its terminals grounded, and the other clamped under conductorterminal 31 and 32, choosing the ones connected to supply lines.

The various connectors 72 and 73 may be varied according to the natureof the service conductors 36 and 37. Two considerations are important:One is that there be very firm clamping of the conductors to theconnectors and of the connectors to the terminal block conductors 31 and32. The other is that the connectors 72 and 73 be separable from theterminal block conductors 31 and 32 and be adaptable to differentangular positions with respect thereto. This latter is because of greatstiffness of the heavy conductors used for the extremely heavy loads forwhich the meter combination is designed. These considerations aresatisfied by providing the terminal clamps of the solid block typeshown, having at one end one or more sockets (with lateral clampingscrews unless compression fittings are used) for the conductors and atthe other end a flat shank 77, which may be firmly clampedto itsappropriate terminal block conductor 31 or 32 by a nut on securing screw78. If all service conductors enter at the bottom, one set can extend upbehind the meter to long-shanked terminal connectors 72 (FIG. 9) eachprovided with a rib 90 to prevent its swinging, thereby maintainingadequate clearance from grounded parts. Neutral conductors such as 79are connected together, as by a multiple connector 80, and groundingconductor 85 may be connected to connector 83 by its own connector clamp86.

SHIFTABLE VOLTAGE LINKS The direction of the current flow in the bar 26at a given instant, and hence the direction of current flow through theaperture of the current transformer 28, depends on whether the meter istop fed or bottom fed. That is, it depends on whether the conductorsleading from the utility lines enter the bottom of the meter box throughconduit 16 or the top through conduit 17. In order that the disk 18 willrotate in the right direction, under both circumstances, it is necessaryto be able to reverse the connections of the voltage coil 23. This isaccomplished by shifting the links 81 seen in FIG. 6. Usually themanufacturer will position these links in the upper position shown inFIG. 6, because that is correct for the more common top fed meter boxwiring. As seen in FIG. 6, the links 81 in this upper position connectcentral terminals 82 with upper terminals 83. As seen in FIG. 5, thecentral terminals 82 are the ones to which the leads 84 from voltagecoil 23 are connected. If the meter is to be used in a bottom fed box,the screws of FIG. 6 are loosened and the links 81 are swung to bridgebetween center screws 82 and lower screws 86.

For the occasional installation having supply and load conductorsentering the box at the same end, one set of connectors may be availablewith sockets opening on a side. If these connectors are somewhathorizontally disposed, conductors clamped in them can extend generallyvertically to pass behind the meter.

The respective connections for the upper screws 83 and the lower screws86 are represented in FIG. 6 by broken lines. The reverse connectionscan be easily recognized by seeing that the right-hand screw 83 isconnected to conductor 27, while the right-hand screw 86 is connected toconductor 26. In each instance, the connection is through ascrew-tightened spacer 49.

It may also be observed that with each position of the links 81, theconnection to the proper bar 26 and 27 is made on the supply side of thetransformer 28. This avoids charging the consumer for the power requiredto energize the voltage coil of his meter. Thus, if we assume topfeeding, the connection of conductor 26 to the external power supplylines is by its upper or a terminal 29, and if we follow conductor 26from that point we see that before it passes through the currenttransformer 28 we come to the screw 48 by which conductor 26 is nowconnected to the voltage coil through terminal 83, link 81 and terminal82. If, however, the lower or b terminal 29 were connected to the sourceof supply we would follow from that point in the opposite direction butagain before reaching ACHIEVEMENT The achievements of this invention aremost important in the areas of economy and convenience. Instead of agreat deal of expensive field service and material costs for installinga separate current transformer and its connections to the meter, andexpensive supervision and checking to be sure that this complex task isdone right, nearly everything is done by more efficient factoryoperations, and with novel structural arrangements which, even asidefrom factory efficiency, minimize material and labor costs. The factoryproduced meter unit, complete with built-in current transformer, withits primary winding conductors already installed, can be mounted andconnected in the meter box, provided with the matching terminal blockfacilities of this invention, with much the same ease and certainty ofcorrectness as in the case of the more simple and common directmetering. In its preferred form, the meter and meter box combinationeven automatically provides an indication when it is in its out ofservice position. Easily shifted potential links provide for thenecessary reversal of the current coil Connections if the supply andload conductors leading to the meter box are reversed from their usualpositions, the same links providing a disconnect position desired formeter testing.

Another important achievement, one which could be of growing importance,is improved dependability of metering accuracy. Using this invention,the meter and current transformer combination is naturally calibrated asa unit. Aberrations of the current transformer from its expected performance which would cause inaccurate metering if connected to a meterpreviously calibrated to accuracy will not have that effect now.Instead, the calibrating adjustment of the meter proper in thecombination will inevitably adjust it to compensate for the aberrationof its associated current transformer. It is the combination, just as itwill be used, which is calibrated to accuracy. The widely used phantomload energization of the meter can be used because the test links areturned to isolate the voltage coil from the conductor bars 26 and 27.The heavy test amperage through the bars 26 and 27 is thus at a muchlower voltage than normal voltage impressed on the voltage coil.

The U-shaped conductor bars permit terminal block facilities which aresimple but nevertheless have correct terminals in proximity to oneanother for connection by a simple bypass. This importantproximity-for-by-pass could also be achieved (and in polyphase use ofthis invention may have to be achieved) by complex terminal blockfacilities, in which case straight conductor bars may be used to carrythe current through the core of the built-in current transformers.

Because the secondary coil 58 of the current transformer is permanentlyconnected to the current coil 24, there is no need for expensive shortcircuiting switches which were previously an important safety measurebecause of high voltage such a secondary coil develops if its circuit isopen while it is energized.

The spacing difference between the upper terminal bolts 33 on the onehand and the lower terminal bolts 33 on the other hand preventsupside-down mounting of meters, one method of stealing electricalenergy.

lclaim:

l. A self contained proportional watt-hour meter for application toterminal facilities of the circuit to be metered comprising a meterelement including a voltage coil and a current coil and having securedat its rear side a current transformer including a core of magneticmaterial forming a closed circuit, a secondary winding on the core andhaving leads connecting it to the current coil of the meter element, anda heavy conductor extending through the core to form the primary windingof the current transformer, both ends of the heavy conductor beingterminals exposed at the rear of the meter for making contact withseparate terminal block conductors adapted for connection to heavysupply and load conductors, respectively.

2. A self contained proportional watt-hour meter for application toterminal facilities of the circuit to be metered comprising a meterelement including a voltage coil and a current coil and having securedat its rear side a current transformer including a core of magneticmaterial forming a closed circuit, a secondary winding on the core andhaving leads connecting it to the current coil of the meter element, anda heavy U- shaped conductor extending through the core to form theprimary winding of the current transformer, both ends of the heavyconductor being terminals exposed at the rear of the meter at one sidethereof for making contact with separate terminal block conductorsadapted for connection to supply and load conductors, respectively.

3. A self contained proportional watt-hour meter for application toterminal facilities of the circuit to be metered comprising a meterelement including a voltage coil and a current coil and having securedat its rear side a current transformer including a core of magneticmaterial forming a closed circuit, a secondary winding on the core andhaving leads connecting it to the current coil of the meter element, anda pair of heavy U-shaped conductors partially overlapping one anotherwith their respective pairs of ends on opposite sides of the meter andeach heavy conductor having one of its legs extending through the coreof the transformer to serve as a primary winding thereof, the ends ofeach heavy conductor being terminals exposed at-one side and to the rearof the meter for connection to separate terminal block conductorsadapted for connection to supply and load conductors, respectively.

4. A self contained proportional watt-hour meter according to claim 3 inwhich the mounting of the two heavy conductors each includes a pair ofvoltage connections electrically on opposite sides of the transformercore each connected to its own terminal, with the terminals arranged inpairs; the voltage coil being connected to additional terminalsintermediate said pairs which in turn are alternatively conductable byshiftable links to one pair or another pair of said terminals, theconnections between the conductors and the terminals being such thatshifting the links reverses the relative polarity through the voltagecoil.

5. A self contained proportional watt-hour meter according to claim 3 inwhich the meter element is mounted on the front of a base plate and themounting of the two heavy conductors on the rear of the base plate eachincludes a post including a voltage connection extending through thebase plate.

6. A self contained proportional watt-hour meter for application totenninal facilities of the circuit to be metered comprising a meterelement including a voltage coil and a current coil and having securedat its rear side a current transformer including a core of magneticmaterial forming a closed circuit about a horizontal axis, a secondarywinding on the core and having leads connecting it to the current coilof the meter element, and a pair of heavy conductors extendinghorizontally from first ends thereof through the core, thereby partiallyoverlapping one another, at least one of the heavy conductors alsoextending vertically to provide a vertical spacing of the ends exposedat one side and to the rear of the meter for connection to separateterminal block conductors adapted for connection to supply and loadconductors, respectively.

7. A self contained proportional watt-hour meter for application of thecombined unit to terminal facilities of the circuit to be meteredcomprising a meter element including a voltage coil and a current coiland having secured to it a current transformer including a core ofmagnetic material forming a closed circuit, a secondary winding on thecore and having leads connecting it to the current coil of the meterelement, and a heavy conductor secured to the unit in a substantiallyfixed relation with respect to the core and extending through the coreto form the primary winding of the current transformer, both ends of theheavy conductor being terminals exposed at the rear of the meter formaking contact with separate terminal block conductors adapted forconnection to supply and load conductors, respectively.

8. A self-contained proportional watt-hour meter for application toterminal facilities of the circuit to be metered comprising a meterelement including a voltage coil and having secured at its rear side acurrent transformer including a core of magnetic material forming aclosed circuit, a secondary winding on the core and having leadsconnecting it to the current coil of the meter element, and heavyconductors carried by the meter element and of which at least oneextends through the core to form the primary winding of the currenttransformer, both ends of each heavy conductor being terminals exposedat the rear of the meter for making contact with separate terminal blockconductors adapted for connection to heavy supply and load conductorsrespectively; and connections normally maintaining the voltage coilconnected between said heavy conductors.

9. The self contained proportional watt-hour meter of claim 8 in whichconnections for the voltage coil include means for reversing itsconnections and for disconnecting it from across the heavy conductorsduring calibration.

10. The combination of the self contained proportional watt-hour meterof claim 8 and a terminal block means comprising two pairs of heavyterminal conductors spaced for receiving the meter terminals havingconnectors for clamping heavy service conductor and each pair havingportions exposed in proximity for application of a bypass to them.

11. The combination of terminal block means and a self containedproportional watt-hour meter for application to that means,

the meter comprising a meter element including a voltage coil and acurrent coil and having secured at its rear side a current transformerincluding a core of magnetic material forming a closed circuit, asecondary winding on the core and having leads connecting it to thecurrent coil of the meter element, and a heavy U-shaped conductorextending through the core to fomt the primary winding of the currenttransformer, both ends of the heavy conductor being terminals exposed atthe rear of the meter on one side thereof for making contact withseparate terminal block conductors adapted for connection to heavysupply and load conductors, respectively;

and the terminal block means comprising a pair of heavy terminalconductors spaced one above the other to receive the terminals of themeter, having connectors for clamping heavy service conductors, andhaving portions exposed in proximity for application of a bypass tothem.

12. The combination of a self contained proportional watthour meter forapplication to terminal facilities of the circuit to be meteredcomprising a meter element including a voltage coil and a current coiland having secured at its rear side a current transformer including acore of magnetic material forming a closed circuit, a secondary windingon the core and having leads connecting it to the current coil of themeter element, and a pair of heavy U-shaped conductors partiallyoverlapping one another with their respective pairs of ends on oppositesides of the meter and each heavy conductor having one of its legsextending through the core of the transformer to 10 serve as a primarywinding thereof, the ends of each heavy conductor being terminalsexposed at one side and to the rear of the meterfor connection toseparate terminal block conductors adapted for connection to supply andload conductors, respectively, and

a terminal block means comprising two pairs of heavy terminal conductorsspaced for receiving the meter terminals having connectors for clampingheavy service conductor and each pair having portions exposed inproximity for application of a bypass to them, the terminals beingaccessible outwardly from the meter and being clamped together by screwmeans.

13. The method of manufacturing an accurate watt-hour meter comprisingconstructing a combined meter and current transformer unit forapplication of the combined unit to terminal facilities of the circuitto be metered comprising a meter element including a voltage and acurrent coil and having secured at its rear side a current transformerincluding a core of magnetic material forming a closed circuit, asecondary winding on the core and having leads connecting it to thecurrent coil of the meter element, and a heavy conductor forming a fixedpart of the unit and extending through the core to form the primarywinding of the current transformer, both ends of the heavy conductorbeing terminals exposed at the rear of the meter for making contact withseparate terminal block conductors;

calibrating said combined unit by steps including a test run of thecombined unit with a test amperage flowing through said conductor, andthereafter retaining the combined unit intact for installation.

14. The method according to claim 13 in which the voltage coil isconnected to test voltage while temporarily disconnected from across thecircuit of said heavy conductor, and in which a lower-voltage phantomload is connected through the heavy conductor.

1. A self contained proportional watt-hour meter for application toterminal facilities of the circuit to be metered comprising a meterelement including a voltage coil and a current coil and having securedat its rear side a current transformer including a core of magneticmaterial forming a closed circuit, a secondary winding on the core andhaving leads connecting it to the current coil of the meter element, anda heavy conductor extending through the core to form the primary windingof the current transformer, both ends of the heavy conductor beingterminals exposed at the rear of the meter for making contact withseparate terminal block conductors adapted for connection to heavysupply and load conductors, respectively.
 2. A self containedproportional watt-hour meter for application to terminal facilities ofthe circuit to be metered comprising a meter element including a voltagecoil and a current coil and having secured at its rear side a currenttransformer including a core of magnetic material forming a closedcircuit, a secondary winding on the core and having leads connecting itto the current coil of the meter element, and a heavy U-shaped conductorextending through the core to form the primary winding of the currenttransformer, both ends of the heavy conductor being terminals exposed atthe rear of the meter at one side thereof for making contact withseparate terminal block conductors adapted for connection to supply andload conductors, respectively.
 3. A self contained proportionalwatt-hour meter for application to terminal facilities of the circuit tobe metered comprising a meter element including a voltage coil and acurrent coil and having secured at its rear side a current transformerincluding a core of magnetic material forming a closed circuit, asecondary winding on the core and having leads connecting it to thecurrent coil of the meter element, and a pair of heavy U-shapedconductors partially overlapping one another with their respective pairsof ends on opposite sides of the meter and each heavy conductor havingone of its legs extending through the core of the transformer to serveas a primary winding thereof, the ends of each heavy conductor beingterminals exposed at one side and to the rear of the meter forconnection to separate terminal block conductors adapted for connectionto supply and load conductors, respectively.
 4. A self containedproportional watt-hour meter according to claim 3 in which the mountingof the two heavy conductors each includes a pair of voltage connectionselectrically on opposite sides of the transformer core each connected toits own terminal, with the terminals arranged in pairs; the voltage coilbeing connected to additional terminals intermediate said pairs which inturn are alternatively conductable by shiftable links to one pair oranother pair of said terminals, the connections between the conductorsand the terminals being such that shifting the links reverses therelative polarity through the voltage coil.
 5. A self containedproportional watt-hour meter according to claim 3 in which the meterelement is mounted on the front of a base plate and the mounting of thetwo heavy conductors on the rear of the base plate each includes a postincluding a voltage connection extending through the base plate.
 6. Aself contained proportional watt-hour meter for application to terminalfacilities of the circuit to be metered comprising a meter elementincluding a voltage coil and a current coil and having secured at itsrear side a current transformer including a core of magnetic maTerialforming a closed circuit about a horizontal axis, a secondary winding onthe core and having leads connecting it to the current coil of the meterelement, and a pair of heavy conductors extending horizontally fromfirst ends thereof through the core, thereby partially overlapping oneanother, at least one of the heavy conductors also extending verticallyto provide a vertical spacing of the ends exposed at one side and to therear of the meter for connection to separate terminal block conductorsadapted for connection to supply and load conductors, respectively.
 7. Aself contained proportional watt-hour meter for application of thecombined unit to terminal facilities of the circuit to be meteredcomprising a meter element including a voltage coil and a current coiland having secured to it a current transformer including a core ofmagnetic material forming a closed circuit, a secondary winding on thecore and having leads connecting it to the current coil of the meterelement, and a heavy conductor secured to the unit in a substantiallyfixed relation with respect to the core and extending through the coreto form the primary winding of the current transformer, both ends of theheavy conductor being terminals exposed at the rear of the meter formaking contact with separate terminal block conductors adapted forconnection to supply and load conductors, respectively.
 8. Aself-contained proportional watt-hour meter for application to terminalfacilities of the circuit to be metered comprising a meter elementincluding a voltage coil and having secured at its rear side a currenttransformer including a core of magnetic material forming a closedcircuit, a secondary winding on the core and having leads connecting itto the current coil of the meter element, and heavy conductors carriedby the meter element and of which at least one extends through the coreto form the primary winding of the current transformer, both ends ofeach heavy conductor being terminals exposed at the rear of the meterfor making contact with separate terminal block conductors adapted forconnection to heavy supply and load conductors respectively; andconnections normally maintaining the voltage coil connected between saidheavy conductors.
 9. The self contained proportional watt-hour meter ofclaim 8 in which connections for the voltage coil include means forreversing its connections and for disconnecting it from across the heavyconductors during calibration.
 10. The combination of the self containedproportional watt-hour meter of claim 8 and a terminal block meanscomprising two pairs of heavy terminal conductors spaced for receivingthe meter terminals having connectors for clamping heavy serviceconductor and each pair having portions exposed in proximity forapplication of a bypass to them.
 11. The combination of terminal blockmeans and a self contained proportional watt-hour meter for applicationto that means, the meter comprising a meter element including a voltagecoil and a current coil and having secured at its rear side a currenttransformer including a core of magnetic material forming a closedcircuit, a secondary winding on the core and having leads connecting itto the current coil of the meter element, and a heavy U-shaped conductorextending through the core to form the primary winding of the currenttransformer, both ends of the heavy conductor being terminals exposed atthe rear of the meter on one side thereof for making contact withseparate terminal block conductors adapted for connection to heavysupply and load conductors, respectively; and the terminal block meanscomprising a pair of heavy terminal conductors spaced one above theother to receive the terminals of the meter, having connectors forclamping heavy service conductors, and having portions exposed inproximity for application of a bypass to them.
 12. The combination of aself contained proportional watt-hour meter for application to terminalfacilities of the circuit to be metered comprising a meter elementincluding a voltage coil and a current coil and having secured at itsrear side a current transformer including a core of magnetic materialforming a closed circuit, a secondary winding on the core and havingleads connecting it to the current coil of the meter element, and a pairof heavy U-shaped conductors partially overlapping one another withtheir respective pairs of ends on opposite sides of the meter and eachheavy conductor having one of its legs extending through the core of thetransformer to serve as a primary winding thereof, the ends of eachheavy conductor being terminals exposed at one side and to the rear ofthe meter for connection to separate terminal block conductors adaptedfor connection to supply and load conductors, respectively, and aterminal block means comprising two pairs of heavy terminal conductorsspaced for receiving the meter terminals having connectors for clampingheavy service conductor and each pair having portions exposed inproximity for application of a bypass to them, the terminals beingaccessible outwardly from the meter and being clamped together by screwmeans.
 13. The method of manufacturing an accurate watt-hour metercomprising constructing a combined meter and current transformer unitfor application of the combined unit to terminal facilities of thecircuit to be metered comprising a meter element including a voltage anda current coil and having secured at its rear side a current transformerincluding a core of magnetic material forming a closed circuit, asecondary winding on the core and having leads connecting it to thecurrent coil of the meter element, and a heavy conductor forming a fixedpart of the unit and extending through the core to form the primarywinding of the current transformer, both ends of the heavy conductorbeing terminals exposed at the rear of the meter for making contact withseparate terminal block conductors; calibrating said combined unit bysteps including a test run of the combined unit with a test amperageflowing through said conductor, and thereafter retaining the combinedunit intact for installation.
 14. The method according to claim 13 inwhich the voltage coil is connected to test voltage while temporarilydisconnected from across the circuit of said heavy conductor, and inwhich a lower-voltage phantom load is connected through the heavyconductor.